Circular fabric knit on a circular knitting machine is usually delivered from the needle cylinder by two or three delivery rolls disposed beneath the knitting unit and then wound in flattened condition on a take-up roll carried by a take-up unit supported to rotate with the needle cylinder. The rotation of the take-up unit usually drives the delivery rolls and the friction rolls on which the take-up roll is supported by a power transmission mechanism including bevel gears which rotate with rotation of the take-up unit. This power transmission mechanism also usually includes a variable speed pulley mechanism using belts and worm gears. One of the delivery rolls is usually driven by the power transmission mechanism and the other one or two delivery rolls are rotated by means of gears secured to the driven delivery roll.
In this prior art type of drive device, the rate at which the knitted fabric is to be taken up must be determined each time a different type of fabric is knit because the production rate will vary according to the fabric structure, the type of yarn to be used, the size of stitch being formed, and the tension applied to the fabric as it is taken up by the take-up unit. Thus, each time that a different type of fabric is to be knit, the drive device must be adjusted to change the size of the variable speed pulley to compensate for the changes being made in the type o fabric being knit. This adjustment of the size of the variable speed pulley is usually a "hit or miss" procedure and requires several adjustments to obtain the proper fabric take-up rate, a time-consuming operation, and a waste of improperly knit fabric.
To overcome the difficulty of the adjustment of this type of drive device, it has been proposed that a drive motor be fixed on the frame of the take-up unit so as to rotate therewith and to directly drive the delivery rolls so that the fabric is taken up in flat condition on the take-up roll in accordance with the speed at which the drive motor is rotated. However, when the drive motor is rotated with the take-up unit the electrical power supply device for the drive motor must include some type of electrical contact ring with electrical contacts in engagement with the ring for supplying electrical energy to the rotating drive motor. The use of the electrical supply contact ring and the electrical contacts engaging the same can frequently cause electrical problems for controlling the motor because of the occurrence of insufficient contact at the electrical contact points, and the generation of noise and the like. When using a servo motor as the drive motor, the number of electrical contacts used in the power supply device increases to raise the cost thereof.